In semiautomatic or automatic firearms, cartridges which are to be fired are commonly stored in a detachable magazine. The magazine defines an enclosure adapted to contain at least one column of cartridges. The cartridges are loaded into the magazine so as to be located atop a magazine follower which engages a lowermost cartridge in the magazine. A magazine spring is included in the magazine and is compressible between the magazine follower and a bottom portion of the magazine so as to bias the follower and loaded cartridges upwardly in the magazine toward an upper open end. An uppermost cartridge from the magazine is loaded into a firing position in the firearm by cooperation with a slide of the firearm.
The slide is adapted to be moveable from an initial firing position rearwardly with respect to the firearm frame, barrel, and magazine and then return forwardly under a spring biasing force. During the returning forward movement of the slide, the slide contacts and strips the uppermost cartridge from the magazine. Under the contact from the slide and the biasing force from the magazine spring, the cartridge moves upwardly with respect to the magazine and forwardly in the firearm, ultimately reaching a firing position in the firing chamber of the firearm.
When a loaded magazine is first placed in the firearm, the slide may be manually cycled to place the first cartridge from the magazine in the firing position. Thereafter, energy from the fired cartridge is used to cycle the slide to eject the casing of the fired cartridge and load the next cartridge from the magazine into the firing chamber. In this manner, each successive shot fired causes the magazine follower and the column of cartridges to incrementally travel upwardly, and each successive cartridge is fed into the firing position in the firearm until no further cartridges remain in the magazine.
A firearm, such as the superlative Model 1911, may be designed so that when the last cartridge from the magazine is fired and the magazine is thus empty, the slide locks open and does not complete its full cycle of movement. This slide locking gives the operator an important visual indication that the magazine is empty. As well, the operator can often tell by feel that the slide has not made its complete cycle to the rear and then back forward. These indications provided by the slide locking in an open position is crucial in a combat, law enforcement, or personal defense setting in which it is not practical for the operator to keep track of the number of cartridges they have fired from a given magazine. The locked open slide informs the operator that the firearm needs to be reloaded.
The slide lock mechanism for locking the slide in the open position when the magazine is empty may include a lever mounted on the firearm frame. This slide lock lever is mounted so that it may move between a locking position in which it catches on a notch or other feature of the slide, and a retracted position in which the slide is free to cycle. The slide lock lever may be biased in some fashion to the retracted position, and, in some firearms, is moved to the locking position by contact with a portion of the magazine follower. In particular, the slide lock lever may include or be connected to a lug which extends through an opening in the firearm frame into the area of the firearm that receives the upper end of the magazine. As the last cartridge is stripped from the magazine, the follower reaches its uppermost position in the magazine under the biasing force of the magazine spring. At this point, contact between a portion of the follower and the slide lock lug forces the slide lock lever toward its extended, locking position. Then, when the last cartridge from the magazine is fired, the slide moves rearwardly under the force of the discharge but is caught in the open position by contact between the slide lock lever and the notch or other locking feature on the slide.
Manufactured items have dimensions subject to tolerances, such that different manufactured items may have different precise dimensions. The tolerances of each constituent component of a magazine, and of the pistol components which interface with the magazine have may significant variations, which in some case result in adverse tolerance stack ups. With pistols which have adverse tolerance stack ups among the components which interface with the magazine assembly, less than a zero tolerance fit between the mag tube and the area of the follower which engages the slide stop can result in a failure to engage the slide stop in order to activate slide lock subsequent to the final round being fired.
The magazine box and follower may also have adverse tolerance stack ups in the side to side fit of the follower to the mag tube. Combining adverse tolerance stack ups with the magazine components and adverse tolerance stack ups with the components of the pistol which interface with the magazine components serves to compound the negative results of adverse tolerances.
Consequently, a new magazine design which provides for reliable operation and dependable slide lock subsequent to the final round being fired, regardless of tolerances, is desirable.